This invention relates to surface cleaning of particulate contamination associated with microelectronic lithography and manufacturing.
A particular technological challenge for implementing microelectronic lithography and manufacturing is the particulate contamination of surfaces associated with certain processes. For example, although pellicles are employed to protect the masks in conventional lithography, pellicles are not sufficiently transparent for wavelengths produced with extreme UV (EUV) lithography. Hence, particles on these masks print every exposure in this type of lithography. Moreover, various processes associated with EUV have a tendency to generate particles that contaminate other surfaces, in addition to masks.
An example of an application to non-EUV lithography is nano-imprint lithography, which involves a mechanical process of pushing a UV-transmittable quartz mold into a thin film. When the mold is withdrawn, small amounts of contamination from the imprinted area may remain on the mold. When subsequent processing is performed with a contaminated mold, feature resolution decreases and there is potential for any film processed with the contaminated mold to be defective.
Particle production can be limited to a certain extent, but it is unreasonable to expect this production to go to zero. As such, mitigation schemes and cleaning protocols of the various surfaces have been proposed. However, conventional wet cleaning with typical chemicals attacks the sensitive surfaces and, hence, degrades these surfaces overtime and therefore is not compatible with EUV or other low critical dimension semiconductor manufacturing.
Recently, some research groups have proposed using laser-induced plasma cleaning systems to remove particulates from surfaces. In these systems, a laser scans across a surface and is focused near the particle to be removed such that breakdown of the gas occurs, resulting in a plasma. This plasma produces a shockwave that dislodges the particle. The shockwave, however, may damage the surface. Details of such systems are discussed in, for example, I. Varghese and C. Cetinkaya, J. Adhesion Sci. Technol., vol. 18, p. 295 (2004) and A. A. Busnaina, J. G. Park, J. M. Lee, and S. Y. Lou, IEEEISEMI Advanced Manufacturing Conference p. 41 (2003), the entire contents of which are incorporated herein by reference.
Others have proposed using a plasma and gas flow based system to clean contaminated surfaces. This system generates reactive plasma that produces etching radicals, which reduces the adhesion force on the particles and the asperity height, which generally prevents rolling. A gas flow head is then moved across the surface to roll the particles off the surface. However, cleaning of patterned EUV masks is very difficult since rolling particles can fall into trenches or build up next to elevated features. Further details of such systems are described in Y. Momonoi, K. Yokogawa, M. Izawa, J. Vac. Sci. Technol. vol. B22, p. 268 (2004), the entire contents of which are incorporated herein by reference.